氯离子在混凝土管桩中的扩散规律

混凝土管桩在海工环境中广泛使用，管桩内表面为封闭面，外壁常常暴露于氯盐环境中。根据菲克第二定律和管桩的边界条件，采用分离变量法，得到氯离子扩散方程的解析解。该解析解包含稳态解和瞬态解2部分，而稳态解由贝塞尔函数构成，与基于半无限体边界条件的传统解不同。采用该解答计算PHC管桩氯离子扩散，探讨内外半径之比、扩散系数以及钢筋保护层厚度对氯离子扩散的影响。当内外半径之比a/b为1.5时，瞬态解的次?糠炙ゼ跛俾时戎饕-糠衷即螵?倍。

Diffusion Behavior of Chloride Ions in Concrete Pipe Piles

Concrete pipe piles, whose internal surface is usually closed and external one is exposed to chloride environment, are widely used in marine environment. Based on Fick second law and the boundary condition of pipe pile, the analytical solution to chloride diffusion equation was deduced with the method of separation of variables. The solution comprises two parts: a stationary solution consisting of Bessel functions, and a transient solution. This is different from the traditional analytical solution that is based on semi-infinite boundary condition. Applying this result to a typical PHC pipe pile, the diffusion of chloride concentration was analyzed. Furthermore, the effects of the ratio of outer radius and inner radius, diffusion coefficient and protective concrete cover thickness on diffusion of chloride concentration were also discussed. When the ratio of outer radius and inner radius equals 1.5, the decay rate of secondary segment of transient solution is 4 times larger than that of the primary part. This example provides a computational basis for the corrosion of steel bar and some reference for durability design of pipe piles as well.